Jul
28

Click here for Part 1. Click here for Part 2.

In this part of our blog series on OSPF area types, our Area 11 is going to undergo a major flashback! The area is going to be reintroduced to an early 1980′s American stereotype called Valley Girls and their Valspeak. The area is no longer going to be Stubby, but it is going to be like. . .like Totally Stubby! Lets review how we left Area 11 and how things looked when it was just a Stub area:

blogospf

R3#show ip ospf database

            OSPF Router with ID (3.3.3.3) (Process ID 1)

		Router Link States (Area 11)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         7           0x80000005 0x001A23 1
3.3.3.3         3.3.3.3         6           0x80000005 0x00D85C 1

		Net Link States (Area 11)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.1.3     3.3.3.3         6           0x80000004 0x004D5E

		Summary Net Link States (Area 11)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         2.2.2.2         33          0x80000001 0x0075C0
10.10.10.0      2.2.2.2         33          0x80000003 0x0062AA
172.16.10.0     2.2.2.2         33          0x80000003 0x00E181
R3#

R3#show ip route

Gateway of last resort is 192.168.1.2 to network 0.0.0.0

     172.16.0.0/24 is subnetted, 1 subnets
O IA    172.16.10.0 [110/21] via 192.168.1.2, 00:01:23, FastEthernet0/0
     10.0.0.0/24 is subnetted, 1 subnets
O IA    10.10.10.0 [110/20] via 192.168.1.2, 00:01:23, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/0
O*IA 0.0.0.0/0 [110/11] via 192.168.1.2, 00:01:23, FastEthernet0/0
R3#

The Stub area configuration wiped out any Type 4 and Type 5 LSAs in Area 11 and gave us the default route to the Area Border Router (ABR) in order to reach those prefixes. Like way cool, man! OK, now I sound like Scott Morris. :-)

Now lets make that Area 11 Totally Stubby and see what happens. All we need to do is go to the Area Border Router (ABR; R2), and add the no-summary keyword to the previous area 11 stub command. Notice this keyword only needs to be on the ABR. While you could add it to each and every area stub command in Area 11, it would have no effect and the proctor would question your abilities. ;-)

OK. Now that we have made the Totally Stubby configuration, lets examine the OSPF Database and IP Routing table on R3:

R3#show ip ospf database

            OSPF Router with ID (3.3.3.3) (Process ID 1)

        Router Link States (Area 11)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         216         0x80000002 0x002020 1
3.3.3.3         3.3.3.3         215         0x80000002 0x00DE59 1

        Net Link States (Area 11)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.1.3     3.3.3.3         215         0x80000001 0x00535B

        Summary Net Link States (Area 11)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         2.2.2.2         24          0x80000002 0x0073C1

R3#show ip route

Gateway of last resort is 192.168.1.2 to network 0.0.0.0

C    192.168.1.0/24 is directly connected, FastEthernet0/0
O*IA 0.0.0.0/0 [110/11] via 192.168.1.2, 00:11:07, FastEthernet0/0
R3#

Now I am reminded of a famous episode of the American television hit, Seinfeld. We have major shrinkage! Notice the Totally Stubby configuration has gone a step further than the Stub Area config. It not only wiped out the LSA Type 4s and 5s, but it also removed the LSA Type 3s. Those were the Summary LSAs about prefixes within our OSPF domain, but in other areas. In fact, the only LSA Type 3 we have left is the special, default route generated by the ABR. Boy is that route important now. It is the only hope of this router reaching any prefixes outside of the area.

Please join us in the next part of this series where we examine the equally, cleverly-named, Not-So-Stubby Area.


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9 Responses to “OSPF Areas, Part 3, the Totally Stubby Area”

 
  1. Marcio Costa says:

    great explanation, please keep doing it !!

  2. Nadeem Rafi says:

    good and simple …. Its KISS

  3. Martin says:

    Thank you

  4. chris says:

    Hey,

    It would be helpful if you linked prior parts of the series in each post.

    …And thanks!

  5. Hi Chris – great idea – I will do it today.

  6. Mr Ethernet says:

    Cool – when’s part 4??

  7. ciscoboy says:

    Hi, please add the “ospf” tag for both Part 3 and Part 4. Thanks. :)

  8. shehab says:

    thank you

 

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